Field of the Invention
The invention relates to an apparatus for welding together by a laser beam two components that overlap in a subregion of their mutually facing surfaces.
When welding components together, it is known to use not only so-called butt welds but also lap welds. Such lap welds, in which the components to be joined together overlap in a subregion of their mutually facing surfaces, are suitable in particular for the use of laser welding methods, since great welding depths with at the same time low heat input and an associated high welding quality can be achieved with a laser beam with high welding speeds. For production and commercial reasons, in the case of lap welds the components to be joined together are generally joined by a plurality of spaced-apart spot welds.
An apparatus for spot welding with a laser beam is known, for example, from European Patent 0 440 002 B1. In the case of the known apparatus, a laser welding head is disposed at the free end of a multi-jointed robot arm. With such a robot arm, the welding head can be guided freely over the surface of the component to be joined and stopped at the positions predetermined for spot welding. For this purpose, the welding head is positioned with the aid of the robot arm by a fixing element, by which the two components are pressed firmly against each other in an overlapping region. The fixing element includes two clasp-like clamping elements, one of which is provided with a central opening. The laser welding head is positioned and fixed over the central opening. This permits spot welding at a location of the overlapping region at which the components are pressed firmly against each other and as far as possible without any gaps therebetween. With the aid of the robot arm, the laser welding head can be brought successively up to a plurality of spaced-apart clamping elements, in order to ensure the strength of the joint by a multiplicity of such spot welds.
It is known from U.S. Pat. No. 4,654,505 to provide, instead of a single laser welding head which can be guided by a robot arm, a plurality of laser welding heads which are disposed on a clamping apparatus and into which the laser beam produced by a laser and spreading out freely is fed at successive times by adjustable mirrors.
However, the spot weld produced by the laser beam has a relatively small diameter, with the result that the required strength of the joint is ensured only by a correspondingly high number of spot welds. This entails increased expenditure with respect to process engineering, which calls into question the cost-effectiveness of spot-welding methods carried out with a laser beam.
German Patent 43 31 827 C1 discloses an apparatus for securing a screwed joint by a multiplicity of microwelded points produced by a laser beam and provided around the circumference of the screw head or the nut. In the case of this known apparatus, two or more part-beams are formed by a beam splitter disposed in the laser welding head, with the result that a plurality of microwelded points are produced simultaneously. An additional turning of the entire optical configuration within the laser welding head permits multiple setting of the microwelded points around the circumference of the screwed joint, by a single stationary laser welding head.
Japanese Laid-Open Application No. JP 58-68492 discloses an apparatus for spot welding by a laser beam, in which a rotatably mounted deflecting and focussing optical system is disposed in the laser welding head and is turned during the welding operation, with the result that the welded points form a circular line and the strength of the weld is increased.